PHP Code i need help in editing it please

well i have a PHP code which i dont know how to edit it as the way i want , it is working that way but not like i want it have some errors or so i need to be fixed and want to add some stuff to it too

here is the code :

<?php
//--------------------------Set these paramaters--------------------------

// Subject of email sent to you.
$subject = 'Results from Customer Comments';

// Your email address. This is where the form information will be sent.
$emailadd = 'email@.com';

// Where to redirect after form is processed.
$url = 'http://mythankyoupage';

// Makes all fields required. If set to '1' no field can not be empty. If set to '0' any or all fields can be empty.
$req = '1';

// ----------------------------------------------------
$text = "Results from form:\n\n";
$space = ' ';
$line = '
';
foreach ($_POST as $key => $value)
{
if ($req == '1')
{
if ($value == '')
{echo "$key is empty";die;}
}
$j = strlen($key);
if ($j >= 20)
{echo "Name of form element $key cannot be longer than 20 characters";die;}
$j = 20 - $j;
for ($i = 1; $i <= $j; $i++)
{$space .= ' ';}
$value = str_replace('\n', "$line", $value);
$conc = "{$key}:$space{$value}$line";
$text .= $conc;
$space = ' ';
}
mail($emailadd, $subject, $text, 'From: '.$emailadd.'');
echo '<META HTTP-EQUIV=Refresh CONTENT="0; URL='.$url.'">';
?>

so this code is already working as i refereed before
in my webpage the customer comments i have
First Name , Last Name , Email and Comments Fields and submit ( to send those comments to my email ) and reset ( to clear all the data that the customer entered and start over again ) buttons

so when i test the code , if i fill all the fields it direct me to my thank you page so this is the only working part.

when i leave any field empty or all of them empty it automatic redirect me to a page i didnt create saying that this field is empty , but it still send the email to me with the empty fields.

so what i want is if i leave any field empty there is an error pages i created to each field saying that this field is empty , and having the logo of the website and stuff like that and that this customer need to go back which there is a link in the page already created to go back to the customer comments page.
and to send automatic email to the customer that i will be in touch with asap
and to add an image verification ( to control the spam ) if that is possible but actually i dont know how to do it yet..

hope this was clear this time , thanks for your time appreciate any help.

 

Here is a nice tutorial, you can download the script too...
http://tutorialzine.com/2009/09/fancy-contact-form/